The need for high performance, high capacity information technology systems is driven by several factors. In many industries, critical information technology applications require outstanding levels of service. At the same time, the world is experiencing an information explosion as more and more users demand timely access to a huge and steadily growing mass of data including high quality multimedia content. The users also demand that information technology solutions protect data and perform under harsh conditions with minimal data loss. And computing systems of all types are not only accommodating more data but are also becoming more and more interconnected, raising the amounts of data exchanged at a geometric rate.
To address this demand, modern data storage systems (“storage systems”) are put to a variety of uses. For example, they are coupled with host systems to store data for purposes of product development, and large storage systems are used by financial and other institutions to store critical data in large databases.
Fibre Channel is a high performance, serial interconnect standard for bidirectional, point-to-point communications between servers, storage systems, workstations, switches, and hubs. Fibre Channel standards are described by the Fibre Channel Industry Association (FCIA) (http://www.fibrechannel.org).
As Fibre Channel technology advances, an increase in the data transmission speed of the Fibre Channel links becomes increasingly desirable. For example, a new Fibre Channel standard exists that discloses a 4.250 gigabytes per second (Gb/s) data rate (“4 G”), which is an increase from a well established 2.1250 Gb/s data rate (“2 G”).
A Fibre Channel (“FC”) disk drive compliant with the SFF-8045 rev. 4.7 standard (“SFF-8045”) has Enable Bypass signals −ENBL BYP CH1 and −ENBL BYP CH2 that control Port Bypass Circuits (PBC) located external to the drive. The PBC allows an FC loop to remain functional in the event of a drive failure or removal. Signal −ENBL BYP CH1 controls the PBC for FC channel 1, and signal −ENBL BYP CH2 controls the PBC for FC channel 2. When these Enable Bypass signals are asserted (low), the PBC bypasses the drive on the associated channel.
Further in accordance with SFF-8045, a −DRIVE PRESENT signal (“drive insert” or “drive inserted” signal) is connected to the drive's ground plane. In an enclosure receiving the drive, a backplane can optionally use the signal to passively detect the presence of the drive by using a detection circuit connected to a tie up resistor. When the drive is not installed, the detection circuit can detect the signal provided through the tie up resistor. When the drive is installed, the signal is grounded through the drive's ground signal and the grounded state can be detected by the detection circuit.
Further in accordance with SFF-8045, a FAULT LED OUT (“Fault LED”) signal is driven by the drive when the drive has established or detected any of the following conditions.
The drive is asserting both of the Enable Bypass signals.
The drive has detected an internal failure.
The drive has been instructed by the host to turn on the Fault LED (light emitting diode).
Electrically, the Fault LED signal can pull down the cathode of an LED using an open collector or open drain driver circuit. The anode is attached to an appropriate supply through a current limiting resistor. The LED and the current limiting resistor are external to the drive.
The Enable Bypass signals are passively enabled when the drive is inserted and remain enabled until the drive has performed appropriate internal initialization and has determined that it can communicate at a specified data rate on the FC channels.